In the above program, GX IEC Developer considers that each program routine which carries out
a specific task to be a POU or program organisation unit.
Each POU can be written using any of the supported editors i.e. LD, IL, FBD, SFC, ST as shown
below:
Overall Project Configuration illustrating POU integration using SFC, FBD, IL, LD and MELSEC
IL and ST format programs.
POU Pool
A Project will consist of many POU’s, each providing a dedicated control function and held in a
POU Pool. Each POU could be written in any of the IEC editors. Therefore in any given project,
the best language for the required function can be chosen. The compiler will assemble the pro
-
ject into code the PLC can understand but the user interface remains as written.
In this way, perhaps complicated interlocking routines, could be written in a ladder POU, whilst
complex calculations or algorithms, might be better suited to one of the textual, or FDB editors.
It is the choice of the designer/user but this environment allows flexibility.
Software Structure and Definition of Terms Programming
3-4 MITSUBISHI ELECTRIC
Typical PLC program event sequence
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